Thousands of medical researchers around the world use VTK -the Visualization Toolkit- an open-source, freely available software development toolkit providing advanced 3D interactive visualization, image processing and analytics algorithms. They either use VTK directly in their in-house research applications or indirectly via one of the multitude of medical image analysis and bioinformatics applications that is built using VTK: Osirix, 3D Slicer, BioImageXD, MedINRIA, VR-Render, GIMIAS, SCIRun, VolView, IGSTK, and others. Furthermore, VTK also provides 3D visualizations for clinical applications such as BrainLAB's Vector Vision surgical guidance system. VTK has been downloaded many hundreds of thousands of times since its initial release in 1993. Considering its broad distribution and prevalent use, it can be argued that VTK has had a greater impact on medical research, and patient care, than any other open-source visualization package. This proposal is in response to the crescendo of requests we have been receiving from the VTK medical community. The aims are as follows: 1. Update the VTK graphics infrastructure to support efficient representation and rendering of large data, visualizing data over the web and on mobile platforms, and interactively exploring data using 3D widgets. 2. Manage the growth of VTK and its large open-source community by enabling multiple channels whereby code can be easily contributed, discovered, downloaded, and used as modular extensions to VTK. 3. Conduct targeted outreach to maximize the impact of the proposed VTK enhancements on the medical community. We will work collaboratively with five world-leading research labs throughout the proposed process, including the Virtual Lung Project at The University of North Carolina at Chapel Hill, the Institute for Computational Medicine at Johns Hopkins University, and three other labs.